1. The Field of the Invention
The present invention relates to an arrangement for reflecting heat radiation, which comprises an especially transparent substrate such as a glass or glass ceramic substrate, which has a heat reflecting metal oxide layer and, if necessary, other metal oxide layers on at least one side of the substrate. It also relates to a process for making the arrangement and to its uses.
2. The Related Art
Many materials, and indeed both opaque and transparent substrates, e.g. glass, may be provided with new properties by applying layers to their surfaces. Thus e.g. coatings are known, which are transparent for visible light, but only have limited transparency for radiation in the infrared range and the UV range of the spectrum. These types of articles or arrangements are used in glass for building purposes, in industrial plants, fireplaces, baking ovens or even vehicle windows.
For example, wood-fired fireplaces for private use are currently equipped with ROBAX® viewing window panes (from SCHOTT AG, Germany). These fireplaces currently have a comparatively high heating capacity so that a considerable fraction of the heat produced is delivered through the viewing window pane. This is desired when the fireplace is put into operation, since much heat should be delivered to the room at the start of the heating, so that it is heated as rapidly as possible.
On the other hand, considerable heat should be produced so that the fire reaches a controlled combustion state as quickly as possible, i.e. the fuel must burn at as high a temperature as possible. If the fireplace has reached the desired combustion capacity, however a large fraction of the heat is delivered through the fireplace viewing window pane and it significantly heats its surroundings, even the floor and objects in the vicinity of the fireplace. If a wood floor or other valuable furnishings are found near the fireplace window pane, more or less strong aging processes can occur depending on the type of wood.
Usually the fireplace viewing window pane is at temperatures of definitely more than 250° C. in operation. The fireplace viewing window pane is thus a source of danger for children at play.
Soot and fine dust, nitrogen oxides, carbon monoxide and/or carbon dioxide are produced during the combustion according to the combustion conditions. These products are produced both at the start of the combustion and even when it reaches its nominal or rated heating power.
Moreover the modern fireplace frequently is connected with a central heating system, into which the exhaust gas from the fireplace is conducted so that its excess heat can be used once again. Thus excess heat energy, which would otherwise remain in the fireplace and/or in the surroundings, can be additionally useful.
A glass article, which comprises a transparent heat-resistant flat glass, which is provided with a more or less opaque window, is described in US Published Patent Application 2005/0064205 A1. The average transmission of visible light through this window at wavelengths between 380 and 370 nm is 0.03 to 14% and the average reflectivity is at least 50% in the infrared range at wavelengths of from 1000 to 2500 nm.
A coated glass is described in WO 03/093185, which is especially suitable for photovoltaic cells. This glass has a conductive layer acting as an electrode, which comprises an indium oxide layer doped at least with one or more elements. This layer itself can be coated by a protective layer comprising fine metal or metal nitride. Also the use of this sort of electrode as a heating insulating layer is mentioned in that WO reference.